In recent years, high-pressure treatment has started to be utilized as a method for, among other things, inactivating microorganisms and certain enzymes in foodstuffs, in particular in foodstuffs of a particularly high quality, such as fruit juices and the like. The advantage of high-pressure treatment as compared with the more frequently used heat-treatment method is that the microorganisms and the degrading enzymes in the freshly pressed juice are killed or inactivated without destroying vitamins and flavouring. During heat treatment, on the other hand, the taste and the vitamin contents are changed, which requires additives to restore, as far as possible, the nutritive value and taste of the freshly pressed juice.
A decisive factor for obtaining a good result during the high-pressure treatment is that the substance is maintained under a sufficiently high pressure for a sufficiently long period of time. The pressure and the holding time are chosen in dependence on the properties of the substance to be treated, and the general rule is that the higher the pressure and the longer the holding time, the better the result. Further, the rule applies, within certain limits, that if the holding time is extended, the pressure can be reduced and vice versa. Daring treatment of fruit juices, the pressure is usually set a 1,000-15,000 bar and the holding time can vary between a few seconds and some 10 to 30 minutes.
During high-pressure treatment of liquid substances, a so-called pressure intensifier is used. By pressure intensifier is meant here a device which has a high-pressure chamber in which the substance to be treated is pressurized. The pressurization can be accomplished, for example, by designing one of the end walls of the high-pressure chamber as a high-pressure piston with a certain area, which is insertable into the high-pressure chamber. Outside of the high-pressure chamber this piston is secured to a low-pressure piston with a larger area, arranged in a low-pressure chamber. By supplying a certain pressure to the low-pressure piston, for example hydraulically, a higher pressure is thus obtained inside the high-pressure chamber.
When liquid substances are to be treated by high pressure using the present technique, a quantity of the substance as large as can be contained in the pressure intensifier is supplied thereto. Thereafter, the substance is pressurized to the predetermined pressure and is kept in the pressure intensifier at this pressure for the predetermined period of time. After expiration of the predetermined holding time, the pressure in the pressure intensifier is reduced, whereby the substance is decompressed. When the decompression is completed, the substance is removed from the pressure intensifier and the high-pressure treatment is thereby completed.
During industrial manufacture of, for example, juice, but also of other liquid products, a process is often used in which all treatment steps from the raw material to the finished and packaged product are carried out in one unbroken chain. When high-pressure treatment is applied, the high-pressure treatment is thus included as one link in the process chain. According to the prior art as above, one or up to three pressure intensifiers are used in a process chain. In those cases where two or three pressure intensifiers are used, these can utilize one and the same hydraulic unit for generating the pressure by operating in parallel and with a certain mutual time delay.
Technical Problem
Since industrial manufacture of, for example, juice is carried out by means of a process, that treatment step in the process chain which has the lowest capacity with respect to the treated volume per unit of time becomes limiting to the production capacity of the whole process chain. This fact entails problems during high-pressure treatment using current technique as described above.
A considerable problem is that the volume of the pressure intensifier must be dimensioned in relation to the desired production capacity of the whole process chain. In addition to the high-pressure treatment, the packing process is often that part of the production chain that is limiting to the capacity of the whole process. Normal packing machines for juice today have a capacity of about 6,000 to 12,000 liters per hour. If high-pressure treatment is to have a capacity of 6,000 liters per hour and the predetermined holding time is 5 minutes at a suitable pressure, this means that the pressure intensifier must hold about 500 liters of juice. Further, since the pressure intensifier is to be able to generate extremely high pressures, the manufacturing cost of the pressure intensifier stated in the example is very high. From this follows that in order to maintain the necessary capacity in the high-pressure treatment, a pressure intensifier with a very high machine cost per hour is required. In addition, the pressure intensifier is idle for the most part of the high-pressure treatment, namely, during the whole holding time. This, of course, entails considerable economic disadvantages during high-pressure treatment using current technique.
By utilizing several pressure intensifiers in parallel, connected to one and the same hydraulic unit, the efficiency of the hydraulic unit can be increased somewhat. Still, the need of relatively large pressure intensifiers remains, as does the problem of the pressure intensifiers remaining idle during the holding time.
Further, the need of large pressure intensifiers entails problems as regards the energy consumption. To obtain an optimum capacity during the high-pressure treatment, the cycle times should be minimized. The holding time cannot be reduced unless the pressure is increased, which in turn entails further increased manufacturing costs for the pressure intensifier. Instead, the cycle times can be reduced by reducing the time of the pressurization step. When the pressure intensifier has a large volume, however, this means that the energy required for building up the pressure increases considerably. This in turn leads to high operating costs and to the need of powerful and expensive hydraulic units.
To keep cycle times low, it is important that the pressure intensifier be filled and emptied as quickly as possible. When the pressure intensifier has a large volume, this means pulsating flows with high rates of flow, which leads to fatigue stresses in high-pressure components, such as tubes, elbows and valves.
One further problem with high-pressure treatment according to the current technique resides in the fact that the large quantities of energy which are supplied to the substance during the pressurization cannot be recovered in a simple manner during the decompression of the substance. This, of course, entails higher operating costs than what would have been the case if simple recovery of the energy were possible.
The object of the present invention is, therefore, to provide a method and a device for high-pressure treatment of liquid substances whereby the volume of the pressure intensifier does not have to be dimensioned in relation to the desired treatment capacity and whereby it is possible, in a simple manner, to recover the energy which is supplied to the substance during pressurization of the substance.
The Solution
The above-mentioned object is attained according to the invention by means of a method of the kind stated in the introductory part of the description and characterized in that the limited amount of the substance, after having been pressurized in the pressure intensifier, is conducted while substantially maintaining the predetermined pressure from the pressure intensifier to and via an inlet into a pressure chamber, which contains a predetermined larger quantity of the substance at essentially the same predetermined pressure, and that the substance is maintained at the predetermined pressure for the predetermined time by being brought to pass over a predetermined distance between the inlet and an outlet arranged in the pressure chamber.
During high-pressure treatment according to the invention, the pressure intensifier can be dimensioned to generate a certain capacity flow independently of the required holding time. The attainment of the holding time is, at a certain capacity flow, exclusively dependent on the volume of the pressure chamber. Since the pressure intensifier therefore can be made considerably smaller than according to prior art and since pressure chambers are considerably less expensive to manufacture per unit of volume than pressure intensifiers, the above-mentioned economic and technical problems associated with a large volume of the pressure intensifier are eliminated.
According to a preferred embodiment of the method, the predetermined pressure in the pressure chamber is maintained essentially constant by passing a quantity of the substance from the pressure chamber through the outlet which is essentially equal to the quantity supplied to the pressure chamber through the inlet during the same cycle.
According to one embodiment of the invention, after having passed through the pressure chamber the substance is supplied to a decompressor, in which the supplied quantity of the substance is decompressed in a controlled way.
A further embodiment of the method according to the invention is characterized in that the pressure which is supported by the substance in the decompressor is transferred to the pressure intensifier and there contributes to the pressurization of the limited quantity of the substance which, during the decompression in the decompressor, is located in the pressure intensifier.
The latter embodiment of the invention permits the energy which is released in connection with the decompression of the substance to be recovered and used during the otherwise relatively energy-demanding pressurization. This entails a considerable reduction of the energy consumption compared with the high-pressure treatment according to the current technique.
According to two further embodiments of the invention, the released energy can be transferred from the decompressor either by hydraulic means or by mechanical means.
Further, the method according to one embodiment of the invention permits the substance, after having been conducted from the pressure chamber, to be brought to pass through at least one choke means, instead of being passed to the decompressor. Thereafter, according to an additional embodiment, the substance is caused, after preferably each choke means, to pass through a heat exchanger whereby the temperature of the substance is compensated for the change of temperature which arises when passing through the choke means.
These two latter embodiments permit, if desired, homogenization of the substance to be included as part of the high-pressure treatment and result in the temperature of the substance not being significantly influenced by this homogenization.
The present invention also relates to a device for carrying out the method according to the invention. The device comprises a pressure intensifier operating in a cyclic process and adapted, during each cycle, to pressurize a limited amount of the substance to be treated to the predetermined pressure, and is characterized in that a pressure chamber with an inlet and an outlet, via the inlet and a first high-pressure connection for transporting the pressurized substance, is connected to the pressure intensifier, that the pressure chamber is adapted to maintain the substance at the predetermined pressure during the predetermined period of time by a forced smallest transport distance between the inlet and the outlet, determined by the volume flow and the flow cross section, and that a valve is arranged to close and open the connection between the pressure intensifier and the pressure chamber.
According to two different embodiments, the pressure chamber can either be designed as a tube, whereby the length of the tube constitutes the forcedly determined smallest transport distance between the inlet and the outlet, or as a cylinder.
Further, the pressure chamber according to one embodiment is provided with guide means intended to cause the pressurized substance to cover the forcedly determined smallest distance between the inlet and the outlet. According to one embodiment, this guide means consists of a conduit of flexible material, one end of the conduit being connected to the inlet of the pressure chamber and the other end of the conduit being connected to the outlet of the pressure chamber. Further, according to this embodiment, the conduit has a certain length which corresponds to the forcedly determined smallest distance over which the substance is to pass between the inlet and the outlet. The pressure chamber is filled with a pressure-absorbing medium in which the conduit is embedded. According to another embodiment, the guide means is in the form of a screw which is arranged coaxially with the pressure chamber and which has essentially the same outer diameter as the inner diameter of the pressure chamber. Further, according to still another embodiment, this screw is fixed to a shaft which is coaxial with the pressure chamber and the screw, the shaft being rotatably arranged at the two end walls of the pressure chamber and projecting through at least one of these end walls.
With the aid of the guide means according to the above, the pressurized substance is caused to pass over a certain predetermined distance in the pressure chamber. In this way it is ensured that the substance resides in the pressure chamber for the predetermined holding time. The different embodiments of the guide means all make possible a safe use as well as a simple cleaning and washing-up of the pressure chamber with guide means. In the embodiment with a flexible conduit, the washing-up takes place by flushing washing-up liquid and then rinsing liquid through the conduit, via the inlet and the outlet of the pressure chamber. When a rotatable screw is used as guide means, the washing-up takes place by first filling the pressure chamber with washing-up liquid to a certain level. Then, the screw is caused to rotate by rotating the shaft projecting from the pressure chamber, for example by means of a motor. This causes the washing-up liquid to be rinsed around in the pressure chamber and clean the guide means as well as the inside of the pressure chamber. After washing-up, the pressure chamber is rinsed in the same way with a rinsing liquid.
Yet another embodiment of the invention according to the invention is characterized in that the pressure chamber, via the outlet and a second high-pressure connection for transporting the pressurized substance, is connected to a decompressor, and that a second valve is adapted to close and open the connection between the pressure chamber and the decompressor.
With this embodiment, the substance is allowed to be decompressed in a controlled manner and undesired homogenization of the substance is thus avoided.
According to one embodiment, the two high-pressure connections consist of straight high-pressure tubes. This means a considerable advantage since cross-bores and other geometries, which are disadvantageous in a high-pressure context, are avoided.
According to one embodiment, the decompressor is provided with means for utilizing the pressure which is supported by the substance in the decompressor, these means communicating with pressure-generating means in the pressure intensifier.
This latter embodiment permits the energy which is released in connection with the decompression of the substance to be recovered and used for the otherwise relatively energy-demanding pressurization. This entails a considerable reduction of the energy consumption compared with high-pressure treatment according to the current technique.
Still another embodiment of the device according to the invention is characterized in that the pressure intensifier comprises a first high-pressure chamber for containing the substance to be pressurized, a first high-pressure piston which is displaceable in the first high-pressure chamber and has a first high-pressure area, a first low-pressure chamber for containing a pressure medium, a first low-pressure piston which is displaceable in the first low-pressure chamber and which is fixed to the first high-pressure piston and has a first low-pressure area which is larger than the first high-pressure area, and that the decompressor comprises a second high-pressure chamber for containing the pressurized substance, a second high-pressure piston which is displaceable in the second high-pressure chamber and has a second high-pressure area, a second low-pressure chamber for containing a pressure medium, and a low-pressure piston which is displaceable in this second low-pressure chamber and is secured to the second high-pressure piston and has a second low-pressure area which is larger than the second high-pressure area.
Still another embodiment is characterized in that the means for utilizing the pressure which is supported by the substance in the decompressor comprises the second high-pressure piston, the second low-pressure chamber and the second low-pressure piston, that the pressure-generating means comprise the first high-pressure piston, the first low-pressure chamber and the first low-pressure piston.
By combining the latter embodiments described above, several different possibilities are afforded to recover the energy which is released in connection with the decompression. One such possibility is represented by an embodiment of the invention which is characterized in that the first low-pressure chamber and the second low-pressure chamber consist of a common low-pressure chamber, and that the first low-pressure piston and the second low-pressure piston consist of a common low-pressure piston, the first and second high-pressure pistons being arranged on different sides of this common low-pressure piston.
With the embodiment mentioned above, the pressure which is supported by the substance in the decompressor is transmitted mechanically from the decompressor to the pressure intensifier. When the substance in the decompressor expands, the second high-pressure piston is displaced, whereby also the common low-pressure piston and the first high-pressure piston are displaced. The displacement of the first high-pressure piston thereby contributes to the pressurization of the substance in the high-pressure chamber of the pressure intensifier. If the first and second high-pressure areas are the same, the decompression and the pressurization will proceed until the pressure difference between the pressure of the substance in the decompressor and the pressure of the substance in the pressure intensifier has practically disappeared. For the substance in the pressure intensifier to attain the predetermined pressure, additional pressure must be supplied to the first high-pressure piston. This can be achieved by hydraulically pressurizing the pressure medium in the common low-pressure chamber, on that side of the common low-pressure piston which is opposite to the first high-pressure piston. However, a further embodiment of the invention is characterized in that the first high-pressure area is smaller than the second high-pressure area. In this way, the decompression of the substance in the decompressor results in a higher pressure of the substance in the pressure intensifier. Only a slight additional pressure need to be added to the low-pressure piston to overcome any friction losses. This embodiment thus offers a simple solution to the energy recovery problem during high-pressure treatment.
Another possibility of transmitting the pressure which is supported by the substance in the decompressor is afforded by an embodiment which is characterized in that the first low-pressure chamber is hydraulically connected to the second low-pressure chamber. The pressure intensifier and the decompressor are thus separated but they communicate hydraulically via their respective low-pressure chambers. In the same way as in the embodiment with mechanical transmission of pressure, the predetermined pressure in the decompressor can be caused to contribute to the pressurization of the substance in the pressure intensifier. This is achieved in one embodiment in that the first high-pressure area is smaller than the second high-pressure area and in another embodiment in that the first low-pressure area is larger than the second low-pressure area. The last two embodiments have the advantage that they allow the use of a small and inexpensive hydraulic pump for generating the last pressure increase up to the predetermined pressure.